1. Field of the Invention
The present invention relates to a magnetic transcription device using a master information carrier for recording predetermined information signals in advance on a magnetic recording medium used for a magnetic recording reproduction device having a large capacity and high recording density and also to a method for manufacturing a magnetic recording medium.
2. Description of the Related Art
At present, magnetic recording reproduction devices are being designed to have higher recording density in order to achieve a large capacity with a small size. In the field of a hard disc drive, which is a typical magnetic disc device, a device having an areal recording density of more than 10 Gbits/sqin is commercialized already, and such a rapid progress in the technology can be observed that even the practical use of a device having an areal recording density of 20 Gbits/sqin is predicted to be realized in a year.
As the technical background for enabling such high recording density, significant factors are the improvement in the linear recording density as well as a magneto-resistive element type head that can reproduce a signal with a track width of as small as several xcexcm with excellent S/N characteristics.
Furthermore, along with the development to achieve higher recording density, the demand for a reduction in the amount of floatation for a floating magnetic slider against a magnetic recording medium also is growing, since the possibility of a contact occurring between a disc and a slider is increasing also during floatation. Under such circumstances, the demand for more smoothness for a recording medium is growing.
Now, for a head to scan narrow tracks accurately, the tracking servo technology of the head plays an important role. As for a present hard disc drive employing such tracking servo technology, a servo signal for tracking, an address information signal and a reproduction clock signal etc. are recorded in the magnetic recording medium at a constant angle interval. The drive device identifies and corrects the position of a head by these signals, which are reproduced from the head at a constant time interval, so that the head can scan accurately on the tracks.
Here, as mentioned above, signals such as the servo signal for tracking, the address information signal and the reproduction clock signal serve as reference signals for the head to scan accurately on the tracks. Therefore, the positioning for its writing (hereinafter referred to as a formatting) is required to be performed with high precision. In present hard disc drives, formatting is performed by determining the position of a recording head by using a single-purpose servo device (hereinafter referred to as a servo writer) that uses a high precision position detection device utilizing optical interference.
However, there are the following problems to be solved for performing formatting with the use of the above-mentioned servo writer.
First, a recording by a magnetic head basically is a linear recording based on the relative movement between a magnetic head and a magnetic recording medium. It is necessary to write signals over a large number of tracks, so that the method with the use of a servo writer requires a great amount of time for preformat recording. In addition, since several units of expensive single-purpose servo writers are needed to achieve higher productivity, the cost for preformat recording has become high.
Secondly, an extremely high cost is required for the introduction and maintenance of numerous servo writers. These problems become more serious as the track density is improved and the number of tracks is increased. Therefore, instead of using a servo writer for formatting, a system is proposed in which a so-called master disc on which all the servo information is written in advance is used to perform a surface transcription of the information of the master disc as a whole by overlapping a magnetic disc to be formatted on the master disc and applying an external magnetic field for transcription from the outside.
As one example thereof, a magnetic transcription system is disclosed in JP10(1998)-40544A. According to the system disclosed in this publication, a magnetic portion made of a ferromagnetic material is formed in a pattern corresponding to an information signal on the surface of a base to create a master information carrier, that is, a magnetic transcription master, and the surface of this master information carrier is contacted with the surface of a sheet-type or a disc-type magnetic recording medium on which a ferromagnetic thin film or a ferromagnetic powder-coated layer is formed. Then, by applying a predetermined external magnetic field thereto, a magnetization pattern of the pattern corresponding to the information signal formed on the master information carrier will be recorded on the magnetic recording medium.
An example of the conventional steps performed for initial magnetization and transcription of a magnetic recording medium in such a magnetic transcription system is shown in FIG. 32. Furthermore, FIG. 33 shows the relationship of a distance between a magnetic head gap and the surface of a magnetic recording medium as well as a rotation speed of a magnetic head with respect to the rotational phase of the magnetic head for generating an external magnetic field. The magnetic head is not rotated when the magnetic head approaches to or separates from the magnetic recording medium, and the magnetic head is driven only in the approaching or separating direction. On the other hand, when initial magnetization and transcription are performed, a magnetic field is applied to the magnetic recording medium, so that the magnetic head rotates, centering substantially on the central part of the magnetic recording medium. Therefore, according to the conventional method, the operation of approach and separation of the magnetic head and the rotational operation for initial magnetization and transcription were performed completely independently of each other.
Such a magnetic transcription system involves a method of performing a surface recording of pattern arrays corresponding to information signals formed on a master information carrier as magnetization patterns as a whole, and it is important that the high density information signals are recorded stably over the entire magnetic recording medium.
In the conventional magnetic transcription system as described above, the separation of the magnetic head for transcription is performed with respect to the contact body of the master information carrier and the magnetic recording medium after the magnetic head for transcription is immobilized with respect to the magnetic recording medium, so that there was a problem in that deterioration of a recording signal (a big fluctuation of a reproduction peak level) occurred in a portion corresponding to the separating position of the magnetic head for transcription (the position at the phase of 450 degrees in FIG. 33).
FIG. 34 shows the peak value of a reproduction signal voltage relative to the rotational phase of a magnetic recording medium. The lateral axis in this drawing shows the vicinity of the phase in which the magnetic head is separated, and the values are omitted. This also goes for FIG. 21 to be explained later. FIG. 35 is a waveform of a reproduction signal in a phase in which the magnetic head for transcription is separated. The lateral axis and the vertical axis respectively show the time and the reproduction signal voltage. As indicated by an arrow in FIG. 34, there is a portion where the peak value of the reproduction signal drops. The waveform of the reproduction signal in this portion is shown as FIG. 35. As is clear from FIG. 35, a voltage v2 drops greatly compared to a voltage v1, illustrating that the reproduction signal has deteriorated. Therefore, the ratio of a signal to noise (S/N ratio) drops in this portion, and the rate of errors can be increased.
In the conventional system as described above, a drop in the reproduction signal voltage occurs in the phase in which the magnetic head for transcription is separated. The magnetic transcription recording is performed by an external magnetic field component parallel to the master information carrier. However, in fact, due to the structure of a magnetic head, an external magnetic field component perpendicular to the master information carrier also is applied. The reason why such deterioration of a recording signal as described above arises is that the effect of this vertical component is not cancelled in the phase in which the magnetic head for transcription is separated.
This deterioration of a recording signal in the phase when the magnetic head for transcription is separated tends to increase as the strength of the applied external magnetic field becomes higher. On the other hand, the coercive force of a magnetic recording medium tends to increase along with the further improvement in the recording density, so that the external magnetic field strength to be applied naturally needs to be increased. Therefore, it is considered that the degree of deterioration in the above-mentioned recording signal will become even higher in the future, and the present problem must be solved for a long time to come.
In view of the foregoing problems, it is an object of the present invention to achieve a magnetic transcription with a high degree of reliability in which signal deterioration does not occur in a position where an external magnetic field is removed.
To achieve the above-mentioned object, a magnetic transcription device of the present invention is a magnetic transcription device for transcribing information signals of a master information carrier in a magnetic recording medium by applying a magnetic field generated by magnetic field generating means to a contact body obtained by contacting the master information carrier with a magnetic recording medium having a ferromagnetic layer, the master information carrier including a base on which ferromagnetic bodies corresponding to the information signals are formed, wherein the magnetic transcription device includes driving means for adjusting a distance between the magnetic field generating means and the contact body while rotating the magnetic field generating means relative to the contact body.
According to the magnetic transcription device as described above, an external magnetic field can be applied and removed for transcription of the information signals of the master information carrier in the magnetic recording medium while rotating the magnetic field generating means relative to the contact body, so that the deterioration of reproduction signals from the magnetic recording medium can be prevented.
In the above-mentioned magnetic transcription device, it is preferable that the driving means is designed to shift the magnetic field generating means and a surface of the contact body close to each other, drive at least one selected from the magnetic field generating means and the contact body to rotate taking substantially the central part of the magnetic recording medium as the center of rotation, and thereby rotate the magnetic field generating means relative to the contact body, and that
after the relative rotation is performed at least for one revolution, the magnetic field generating means is separated from the contact body while maintaining the rotational drive. According to the magnetic transcription device as described above, the deterioration of transcription recording signals can be prevented in a phase when the magnetic head is separated, so that uniform transcription recording can be performed over the entire magnetic recording medium.
Furthermore, it is preferable that the magnetic field generating means and the surface of the contact body are shifted close to each other while rotating the magnetic field generating means relative to the contact body such that at least one selected from the magnetic field generating means and the contact body is driven to rotate by taking substantially the central part of the magnetic recording medium as the center of rotation. According to the magnetic transcription device as described above, the deterioration of transcription recording signals can be prevented also when the magnetic head is approaching, so that uniform transcription recording is secured even more over the entire magnetic recording medium.
Furthermore, it is preferable that the driving means can rotate the magnetic field generating means relative to the contact body by driving at least one selected from the magnetic field generating means and the contact body to rotate taking substantially the central part of the magnetic recording medium as the center of rotation in a state in which the magnetic field generating means is in close contact with the contact body, and that
the magnetic field generating means has a magnetic core and a coil for generation of a magnetic field through a current supplied to the coil by current application means, and that
the current application means is designed to gradually reduce a current value to be supplied to the coil after the relative rotation is performed at least for one revolution in a state in which the rotational drive is maintained. According to the magnetic transcription device as described above, the deterioration of transcription recording signals can be prevented when an external magnetic field is removed by the magnetic head, so that uniform transcription recording can be performed over the entire magnetic recording medium.
Moreover, it is preferable that the current application means applies a current value to the coil for generating a necessary magnetic field for the transcription by gradually increasing the current value while performing the rotational drive. According to the magnetic transcription device as described above, the deterioration of transcription recording signals can be prevented when the magnetic head starts to apply an external magnetic field, so that even more uniform transcription recording is secured over the entire magnetic recording medium.
Furthermore, it is preferable that the magnetic field generating means includes a magnetic core made of a ferromagnetic material and a permanent magnet.
Moreover, it is preferable that the magnetic field generating means includes a magnetic core made of a ferromagnetic material and a coil. According to the magnetic transcription device as described above, an external magnetic field can be applied and removed by controlling an electric current to be supplied to the coil.
Next, a method for manufacturing a magnetic recording medium of the present invention is a method for transcribing information signals of a master information carrier in a magnetic recording medium by applying a magnetic field generated by magnetic field generating means to a contact body obtained by contacting the master information carrier with the magnetic recording medium having a ferromagnetic layer, the master information carrier including a base on which ferromagnetic bodies corresponding to the information signals are formed. The method includes
shifting the magnetic field generating means and a surface of the contact body close to each other, driving at least one selected from the magnetic field generating means and the contact body to rotate, rotating the magnetic field generating means relative to the contact body, and
after the relative rotation is performed at least for one revolution, separating the magnetic field generating means from the contact body while maintaining the rotational drive to complete the transcription. According to the method for manufacturing a magnetic recording medium as described above, the deterioration of transcription recording signals can be prevented in a phase where the magnetic head is separated, so that uniform transcription recording can be performed over the entire magnetic recording medium.
In the above-mentioned method for manufacturing a magnetic recording medium, it is preferable that the magnetic field generating means the surface of the contact body are shifted close to each other while rotating the magnetic field generating means relative to the contact body such that at least one selected from the magnetic field generating means and the contact body is driven to rotate taking substantially the central part of the magnetic recording medium as the center of rotation. According to the method for manufacturing a magnetic recording medium as described above, the deterioration of transcription recording signals can be prevented also when the magnetic head is approaching, so that even more uniform transcription recording is secured over the entire magnetic recording medium.
Furthermore, it is preferable that the magnetic field generating means has a magnetic core and a coil for generation of a magnetic field through a current supplied to the coil, and that the transcription is completed by gradually reducing a current value to be supplied to the coil after the relative rotation is performed at least for one revolution in a state in which the rotational drive is maintained. According to the magnetic transcription device as described above, the deterioration of transcription recording signals can be prevented when an external magnetic field is removed by the magnetic head, so that uniform transcription recording can be performed over the entire magnetic recording medium.
Moreover, it is preferable that a current value of the coil for generating a necessary magnetic field for the transcription is applied by gradually increasing the current value while performing the rotational drive. According to the magnetic transcription device as described above, deterioration of transcription recording signals can be prevented when the magnetic head starts to apply an external magnetic field, so that even more uniform transcription recording is secured over the entire magnetic recording medium.